In a lubricating structure of an internal combustion engine, generally, oil is pumped up from an oil pan by an oil pump, and fed to respective portions of the internal combustion engine through oil passages diverging from a main gallery. As this type of lubricating structure of the internal combustion engine, there has been known a lubricating structure of an internal combustion engine in which an oil passage extending toward a crankshaft and an oil passage extending toward various transmission shafts such as a driveshaft are separated (e.g. see JP-A-2015-090146). In the internal combustion engine according to JP-A-2015-090146, a main gallery is formed below the crankshaft, and an oil passage is formed to extend from the main gallery and obliquely upward and rearward toward the driveshaft which is disposed at the rear of the crankshaft. In the internal combustion engine according to JP-A-2015-090146, the oil passage extending from the main gallery toward the various transmission shafts is diverged into parts in the middle, and oil is fed to a bearing of a balancer shaft in an upper portion of the crankcase through one of the diverged parts of the oil passage.